The present invention relates to data transmission systems, and in particular, to a power management technique suitable for a protocol circuit in a data transmission system provided with an IEEE 1394 interface.
Digital AV equipment such as digital televisions (DTV), digital video camera (DVC) and set-top box (STB) is now becoming widespread. As a method for data transmission among the digital AV equipment, an IEEE 1394 standard-compliant serial data transmission is mainly adopted.
On the other hand, a large number of PC peripheral equipment such as CD-ROM drives and DVD drives with IEEE 1394 interfaces are coming along. However, the PC peripheral equipment and the digital AV equipment use different protocols. Therefore, even if the PC peripheral equipment and the digital AV equipment are provided with the same type of IEEE 1394 terminals, data cannot be exchanged directly between them.
Protocols engaged in IEEE 1394 standard-compliant serial data transmission are broadly divided into an AV-oriented type and a PC-oriented type. The AV-oriented protocol (hereinafter, referred to as “AV protocol”) uses an IEEE 1394-compliant isochronous transmission, notably IEC61883 standard. On the other hand, the PC-oriented protocol (hereinafter, referred to as “PC protocol”) uses an IEEE 1394 standard-compliant asynchronous transmission, notably Serial Bus Protocol (SBP)-2 standard.
Conventionally, interface control semiconductor integrated circuits for controlling IEEE 1394 interfaces (hereinafter, referred to as “1394LSIs”) are divided into two types, one is provided with AV protocol circuits and the other is provided with PC protocol circuits. Therefore, in the case of data transmission to both of the AV and PC protocols, it is necessary to use two types of 1394LSIs, i.e., an AV-oriented type and a PC-oriented type. However, recently, there has been an increasing demand for using these two protocols especially in digital AV equipment, and thus a 1394LSI with protocol circuits of both of the AV- and PC-oriented types has been developed.
FIG. 9 shows a configuration of the 1394LSI with the protocol circuits of both of the AV- and PC-oriented types. A 1394LSI 100 includes: a PHY 11 for performing initialization and arbitration of a repeater and an IEEE 1394 bus; a LINK control section 12 for exchanging data with the PHY 11; and a plurality of protocol circuits 13a, 13b and 13c. The protocol circuit 13a is an ISO control section for controlling an isochronous transmission to process AV-oriented data such as MPEG2 data and audio data. The protocol circuit 13b is an authentication control section for performing encryption based on a digital transmission content protection (DTCP) standard on an isochronous packet. The protocol circuit 13c is an SBP-2 control section for controlling an asynchronous transmission and processing PC-oriented data. With the debut of such a 1394LSI with a plurality of protocol circuits, a product cost is reduced due to the reduced number of LSIs, a system configuration is simplified, the time required for the development is reduced, for example, in a data transmission system for an IEEE 1394 standard-compliant transmission of AV- and PC-oriented data.
The plurality of protocol circuits incorporated in the 1394LSI described above are not used at the same time. Nevertheless, clocks are always supplied also to unused protocol circuits, resulting in unnecessary power consumption.
Such 1394LSIs as described above are currently incorporated in stationary digital equipment such as DTV or DVD drives in most cases. Since the stationary digital equipment can be supplied with power from commercial power sources, it is unnecessary to consider power consumption by unused protocol circuits in the stationary digital equipment. However, mobile equipment using, as a recording medium, a device such as a DVD or a HDD handling PC-oriented data is expected to come along in future. The mobile equipment is driven mainly by a battery, and thus power consumption will be a particularly important factor. The power consumption by unused protocol circuits should be avoided especially in 1394LSIs incorporated in such mobile equipment.